1. Field of the Invention
The present invention relates to an image pickup system applied to monitoring, image tracking or the like, a method for controlling the shooting direction of an image pickup device, and a program therefor.
2. Description of the Related Art
Conventionally, for the purpose of remote operation and automatic control of a shooting direction, there has been known a video camera device equipped with a pan pivot mechanism and a tilt pivot mechanism that allow the shooting direction to be changed two-dimensionally. By combining this video camera device with a position controller, the camera can be pointed automatically in a predetermined direction to observe moving images. Several methods may be used for the position controller, such as a servo control method for implementing feedback control based on a difference between a command value to issue a directive on the direction of the camera and its current position, and an open control method for implementing feed control by a predetermined distance by means of a stepping motor or the like.
In addition, automatic tracking can be achieved by detecting a predetermined object such as a person, and controlling the direction of the camera so that the object falls within its screen. As a method for detecting an object, there has been known a method in which the features of an object are extracted from an image to recognize the object, and a method in which the position of the object is detected by using an ultrasonic echo or infrared radiation.
Such a video camera device described above can be used for a tracking video camera device that tracks a child who is moving about, for example, so as not for the child to protrude from the screen, a monitoring system for monitoring a suspicious person, and a system for controlling view angles in a sports relay broadcast on TV. This type of systems usually has a monitor to allow images to be observed in real time. The system also can record images on a recording medium so that the images may be replayed and observed later.
In this type of systems, when images are observed, a situation where switching between the images takes place as the camera moves is always encountered. In order not to give a sense of discomfort to an observer at such a time, there has been proposed a method in which the eye movement of the observer is detected to gradually switch from one image to another image (see e.g. Japanese Laid-Open Patent Publication (Kokai) No. 2000-221953). There has also been proposed the fact that it is effective to add ±2 degrees of a dead band to the movement of a manipulator for the removal of unpleasantness associated with the movement of a tracking camera for fingertip observation when the manipulator is remotely operated (see e.g. “Automatic camera tracking for remote manipulators” proc. Of the 1984. National Topical Meeting on Robotics and Remote Handling in Hostile Environments pp. 383-391, 1984. (hereinafter referred to as “Non-Patent Document”).
However, in the conventional video camera device capable of changing the shooting direction, when the shooting direction is changed, moving images present unnatural movement as the camera moves, and therefore unpleasantness is given to the observer. In particular, since the shooting direction is often switched during tracking operation, if high-speed tracking is performed at several Hz or more of response speed, the observer feels considerable unpleasantness. This unpleasantness may cause some people to feel a symptom like seasickness, called image-sickness.
Additionally, human visual acuity for objects that are moving (so-called dynamic visual acuity) is usually poorer than static visual acuity. More specifically, as shown in FIG. 24, cognitive ability tends to rapidly deteriorate for fast movement. The term of cognitive ability herein represents the relative ability of what percentage of oscillating strings can be recognized, for example. As a result, when a screen oscillates at high speed, the observational ability deteriorates, and long observation causes fatigue.
In connection with this, the method described in the above Japanese Laid-Open Patent Publication (Kokai) No. 2000-221953. is disadvantageous because the method needs a large-scale device to detect the eye movement, which imposes a burden on an observer who puts on the device, and involves expenses. In addition, at the time of switching between images, this method uses an intermediate image to gradually change images, however, the intermediate image is a composite image, and therefore there is no guarantee that the image really represents an actual situation. Accordingly, it is highly likely to give a sense of discomfort to the observer. Incidentally, in the embodiment described in the above Japanese Laid-Open Patent Publication (Kokai) No. 2000-221953, an image to be displayed is animation, not a real image.
On the other hand, the method described in the above non-patent document has a certain effect of reducing image-sickness. However, for fast oscillation that the observer cannot follow, if the oscillation is greater than the dead band, the screen oscillates hard, and therefore the unpleasantness of the observer cannot be removed. Additionally, since the addition of the dead band makes the movement discontinuous, step-like movement is caused near boundaries of drive and stop, and the image is not switched smoothly, and therefore, not all of the sense of discomfort can be wiped out. Additionally, since a given dead band is always provided regardless of the movement of an object to be tracked, the image to be observed is not always optimized.